Spring Boot Web 请求参数之Servlet API

1. Servlet API

• ServletRequest
• HttpSession
• InputStream

1.1 HttpServletRequest

@GetMapping("/request")
public Map<String, Object> request(HttpServletRequest request) {
    Map<String, Object> map = new HashMap<>();
    Map<String, String[]> parameterMap = request.getParameterMap();
    map.put("parameterMap", parameterMap);
    map.put("locale", request.getLocale());
    return map;
}

2. 参数解析原理

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三个核心组件：
Handler
HandlerMapping
HandlerAdapter

2.1 流程

1. DispatcherServlet#doDispatch
2. 在 handlerMappings 找处理请求的 Handler
3. 为 Handler 找一个适配器 HandlerAdapter (RequestMappingHandlerAdapter)
4. 执行目标方法 RequestMappingHandlerAdapter#invokeHandlerMethod
5. 参数解析器 this.argumentResolvers

public class DispatcherServlet extends FrameworkServlet {
    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) {
        // ...
        mappedHandler = getHandler(processedRequest);
        HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
        mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
    }
}

2.2 四种适配器

• RequestMappingHandlerAdapter
• HandlerFunctionAdapter
• HttpRequestHandlerAdapter
• SimpleControllerHandlerAdapter

2.3 执行目标方法

• RequestMappingHandlerAdapter#invokeHandlerMethod
• invocableMethod.invokeAndHandle(webRequest, mavContainer);
• InvocableHandlerMethod#getMethodArgumentValues

// ServletInvocableHandlerMethod
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);

2.4 参数解析器

private HandlerMethodArgumentResolverComposite argumentResolvers;
List<HandlerMethodArgumentResolver> argumentResolvers = new ArrayList<>();

public interface HandlerMethodArgumentResolver {

    boolean supportsParameter(MethodParameter parameter);

    Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
            NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;
}

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2.5 返回值处理器

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